ABSTRACT The Seek, Test, and Treat model holds that broad, consistent treatment with antiretroviral therapy (ART) could lower the level of HIV RNA viral load in the community available for transmission. However, there are myriad challenges to implementing this strategy among released HIV+ incarcerated populations given the frequent discontinuity in care following release. Specifically, many ex-inmates fail to link to community-based HIV care long enough to sustain viral load suppression, or they fail to re-initiate any pre-incarceration linkage. Consequently, HIV+ ex-inmates urgently need interventions to improve their retention in HIV care. Most prior research has been conducted on prisons; however persons in jails have even less opportunity to establish optimal ART regimens, yet face equal disruption of treatment upon release. Far greater numbers pass through jails than prisons. Jailed persons also face frequent recidivism, resulting in a revolving door between jail and the community. The goal of this proposal is to adapt an existing, theory-based intervention to maximize its feasibility and acceptability to HIV+ ex-inmates. We will utilize a randomized design for 176 newly released HIV+ ex-inmates assigned to the intervention and 176 control subjects to implement the intervention and evaluate its effectiveness. The study will be conducted among HIV+ male ex-inmates released from the Los Angeles County Jail System, the largest municipal jail system in the world. The proposed intervention will use individually delivered, peer-based learning approaches to address barriers to and facilitators of HIV care retention among released HIV+ jail inmates. The proposal has two Primary Specific Aims: 1. To examine individual-level and structural-level barriers to HIV care after release from jail, using formative semi-structured interviews with ex-inmates, case managers, and HIV care providers; and to use the information we obtain to inform the adaptation and tailoring of an intervention designed to improve linkage with and retention to HIV care for HIV+ ex-inmates; 2. Using a two-group experimental RCT design, to test the adapted peer-based health system navigation intervention condition for HIV+ inmates upon release from jail compared to a usual care condition, and to evaluate the intervention's effectiveness at improving linkage with and retention in HIV care, self- reported ART adherence, and HIV RNA viral load suppression; Secondarily, we will assess the potential moderating effects of substance abuse, the potential mediating effects of substance abuse treatment, and the program's effects on recidivism, and costs. If successful, cost-effective, and adopted as a broader strategy for all released inmates, the community to which the ex-inmate returns may benefit from reduced overall community viral load, which could augment existing prevention strategies, in addition to improving the ex-inmates' health outcomes.